Anamorphic widescreen is a process by which a comparatively wide widescreen image is vertically expanded to fit into a storage medium (photographic film, for example) with a narrower aspect ratio. Compatible play-back equipment (a projector with modified lens) can then recompress the vertical dimension to show the original widescreen image. This is typically used to allow one to store widescreen images on a medium that was originally intended for a narrower ratio, while using as much of the frame - and therefore recording as much detail - as possible.[1]

The technique originally comes from cinema. A film would be framed and recorded as widescreen, but the picture would be "squashed together" using a specially crafted concave lens to fit into non-widescreen 1.37:1 aspect ratio film. This film can then be printed and manipulated like any other 1.37:1 film stock, although the images on it will appear to be squashed horizontally (elongated vertically) as in a fun-house mirror. An anamorphic lens on the projector in the cinema (a convex lens) corrects the picture by performing exactly the opposite distortion, returning it to its original width and its widescreen aspect ratio.

The anamorphic lens on the projector is a specially crafted convex lens that corrects the picture so that the images on the screen look normal. The optical scaling of the lens to a film medium is considered more desirable than the digital counterpart, due to the amount of non-proportional pixel decimated scaling that is applied to the width of an image to achieve (something of a misnomer) a so-called "rectangular" pixel widescreen image. The legacy ITURec. 601 4:3 image size is used for its compatibility with the original video bandwidth that was available for professional video devices that used fixed clock rates of a SMPTE 259M serial digital interface. One would produce a higher-quality upscaled 16:9 widescreen image by using either a 1:1 SD progressive frame size of 640×360 or for ITURec. 601 and SMPTE 259M compatibility a letterboxed frame size of 480i or 576i.

Similar operations are performed electronically to allow widescreen material to be stored on formats or broadcast on systems that assume a non-widescreen aspect ratio.

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Many commercial cinematic presentations (especially epics – usually with the CinemaScope 2.35:1 optical sound or the older 4-track mag sound 2.55:1 aspect ratio) are recorded on standard 35 mm ~4:3 aspect ratio film[1], using an anamorphic lens to horizontally compress all footage into a ~4:3 frame. Another anamorphic lens on the movie theatre projector ultimately corrects (optically decompresses) the picture. See anamorphic format for details. Other movies (often with aspect ratios of 1.85:1 in the USA or 1.66:1 in Europe) are made using the simpler matte technique, which involves both filming and projecting without any expensive special lenses. The movie is produced in 1.375 format, and then the resulting image is simply cropped in post-production (or perhaps in the theater's projector) to fit the desired aspect ratio of 1.85:1 or 1.66:1 or whatever is desired. Besides costing less, the main advantage of the matte technique is that it leaves the studio with "real" footage (the areas that are cropped for the theatrical release) which can be used in preference to pan-and-scan when producing 4:3 DVD releases, for example.

The anamorphic encoding on DVD is related to the anamorphic filming technique (aka Cinemascope) only by name. For instance, Star Wars (1977) was filmed in 2.35:1 ratio using an anamorphic camera lens, and shown in theaters using the corresponding projector lens. Since it is a widescreen film, when encoded on a widescreen-format DVD the studio would almost certainly use the anamorphic encoding process. Monty Python and the Holy Grail was filmed in 1.85:1 ratio without using an anamorphic lens on the camera, and similarly was shown in theaters without the need for the decompression lens. However, since it is also a widescreen film, when encoded on a widescreen-format DVD the studio would probably use the anamorphic encoding process.

It doesn't matter whether the filming was done using the anamorphic lens technique: as long as the source footage is intended to be widescreen, the digital anamorphic encoding procedure is appropriate for the DVD release. As a sidenote, if a purely non-widescreen version of the analog-anamorphic Star Wars were to be released on DVD, the only options would be pan-and-scan or hardcoded 4:3 letterboxing (with the black letterboxes actually encoded as part of the DVD data). If you were to release a purely non-widescreen version of Monty Python, you would have those options, as well as the additional option of an "open-matte" release, where the film footage that was never visible in theaters (due to use of the matte technique in post-production or in the theatrical projectors) is "restored" to the purely non-widescreen DVD release.

A DVD labeled as "Widescreen Anamorphic" contains video that has the same frame size in pixels as traditional fullscreen video, but uses wider pixels. The shape of the pixels is called pixel aspect ratio and is encoded in the video stream for a DVD player to correctly identify the proportions of the video. If an anamorphic DVD video is played on standard 4:3 television without adjustment, the image will look horizontally squeezed.

Pre-2004 Universal Anamorphic DVD packaging sample. Now used by Sony Pictures Home Entertainment.

Although currently there is no labeling standard, DVDs with content originally produced in a 16:9 aspect ratio are typically labeled "Anamorphic Widescreen," "Enhanced for 16:9 televisions," "Enhanced for widescreen televisions," or similar. If not so labeled, the DVD is intended to fill a 4:3 display ("fullscreen"), and will be letterboxed or panned and scanned.

There has been no clear standardization for companies to follow regarding the advertisement of anamorphically enhanced widescreen DVDs. Some companies, such as Universal and Disney, include the aspect ratio of the movie. Below are how various companies advertise their anamorphic DVD movies on their packaging:

Anchor Bay: "Enhanced for 16:9 TVs;" includes aspect ratio in most cases.

Artisan Entertainment: "16:9 Fullscreen Version" or "Enhanced for 16:9 Television." Since it became part of Lions Gate, the newer reissues include aspect-ratio information on many titles. (This is an unconventional use of the term "fullscreen", which normally refers to a 4:3 ratio.)

An electrically coded video line (referred to as a field) is used in analog video transmission, recording and CRT displays, this can be sampled by a process called digitization which in professional SD video tape recorders is done at a rate of 720 pixels per field. This relates to the bandwidth used in digital serial connections and have come to be inaccurately called "rectangular" pixels. So called "square" pixels used to display 4:3 graphics and text on VGACRTs are at 640×480 which excludes the sync pulses and blanking used in the field output. Therefore, to display a NTSC SD 4:3 capture of 720×480 you would have to crop the 8 pixels that are used for blanking off of each side and then "anamorphic-ally" scale the result to 640×480. Squeezing to create a 16:9 frame only does a good job of delivering widescreen with reasonable quality using standard 4:3 equipment when the compressed bit rate is high enough to avoid compression artifacts being noticed, as they are in a low rate MPEG-2 broadcast.

Blu-ray also supports anamorphic wide-screen, both at the DVD-Video/D-1 resolutions of 720×480 (NTSC) and 720×576 (PAL), and at the higher resolution of 1440×1080 (source aspect ratio of 4:3, hence a pixel aspect ratio of 4:3 = 16:9 / 4:3 when used as anamorphic 16:9). See Blu-ray Disc: Technical specifications for details.

Major digital televisionchannels in Europe (for example, the five major UK terrestrial TV channels of BBC One, BBC Two, ITV, Channel 4 and Channel 5), as well as Australia, carry anamorphic widescreen programming in standard definition. In almost all cases, 4:3 programming is also transmitted on the same channel. The SCART switching signal can be used by a set-top-box to signal the television which kind of programming (4:3 or anamorphic) is currently being received, so that the television can change modes appropriately. The user can often elect to display widescreen programming in a 4:3 letterbox format instead of pan and scan[citation needed] if they do not have a widescreen television.

TV stations and TV networks can also include Active Format Description (AFD) just as DVDs can. Many ATSC tuners (integrated or set-top box) can be set to respond to this, or to apply a user setting. This can sometimes be set on a per-channel basis, and often on a per-input basis, and usually easily with a button on the remote control. Unfortunately, tuners often fail to allow this on SDTV (480i-mode) channels, so that viewers are forced to view a small picture instead of cropping the unnecessary sides (which are outside of the safe area anyhow), or zooming to eliminate the windowboxing that may be causing a very tiny picture, or stretching/compressing to eliminate other format-conversion errors. The shrunken pictures are especially troublesome for smaller TV sets.

Many modern HDTV sets have the capability to detect black areas in any video signal, and to smoothly re-scale the picture independently in both directions (horizontal and vertical) so that it fills the screen. However, some sets are 16:10 (1.6:1) like some computer monitors, and will not crop the left and right edges of the picture, meaning that all programming looks slightly (though usually imperceptibly) tall and thin.

1. ^ The standard 1932 Academy ratio changed the true aspect ratio of the image data to 1.375 when they made space for audio tracks, however, this is close enough to 4:3 that the difference is often glossed over.